Orthopedic implant consisting of a support structure provided with at least an orifice for passing through a fixing screw associated with a nut

ABSTRACT

An orthopedic device having a support structure provided with at least an orifice for a fixing screw associated with a nut; the head of the screw to be pressed on one side of the support, and the nut adapted to be pressed on the other side of the support, in a housing enabling its being integrated at least partly, so as to enable the support structure to be clamped between the screw head and the nut when the screw body has been completely screwed in the receiving bone material. The implantable device includes elements for maintaining the nut in its housing opposite the orifice, and elements for locking the nut in rotation. The contours of the housing and of the nut are dimensioned to provide at least one degree of freedom to the nut in the housing enabling self-centering of the screw and nut.

BACKGROUND OF THE INVENTION

1. Summary of the Invention

The present invention relates to a new orthopaedic implant system of thetype formed of a supporting structure fitted with at least one orificeto let through a fastening screw associated with a nut.

2. Description of the Related Art

Generally speaking, orthopaedic implants, in particular osteosynthesisimplants, include a supporting structure in the form of a plate, a shellor other, fitted with one or of several orifices intended to let throughfastening screw able of being anchored in the receiving bone material.

The general shape and the dimensions of this supporting structure areadapted to the implantation constraints.

There exist a very large number of types of implants which differ inparticular by the presence or not of an interconnection between thescrew head and the supporting structure, to optimise retention of thescrew over a long period of time, and/or the presence of meansconferring to the fastening screw a possibility of angular orientationrelative to the axis of its reception orifice, to enable the practicianposition at best said screw relative to the site of implantation and tothe corresponding spatial constraints.

Good holding quality of the implant is obtained when the supportingstructure is sandwiched between the screw head and a nut, as known fromthe document WO-A-99/09903. But in such a case, the particularinterconnection of the nut with the supporting structure requiresaccurate introduction of the fastening screw so as not to damage thethread of the nut during the screwing operation; and the practician hasno possibility of orienting the screws spatially.

SUMMARY OF THE INVENTION

The present invention provides a new implantable orthopaedic device,simple in its structure, convenient, exhibiting good locking and holdingqualities, and allowing certain possibility of spatial orientation ofthe fastening screw relative to the axis of the reception orifices laidout in the supporting structure.

This orthopaedic implant is of the type formed of a supporting structurefitted with at least one orifice to let through a fastening screwassociated with a nut, the head of said screw being intended for restingon one side of said support, and said nut being intended for resting onthe other side of said support, in a housing which enables at leastpartial integration, to allow clamping said supporting structure betweenthe screw head and the nut, upon complete clamping of the screw body inthe receiving bone material; this implantable device also includes meansfor holding said nut in its reception housing facing the orifice of thesupporting structure, and for locking said nut in rotation.

According to the present invention, the contours of the housing of thesupporting structure and the contours of the nut are sized to confer atleast one degree of freedom to said nut in said housing, therebyenabling self-centring of the fastening screw and of the associated nut,regardless of the admissible orientation of the axis of said screwrelative to the axis of the orifice of the supporting structure.

According to a first possible embodiment, the holding means of the nutin its reception housing are composed of a material rebound closingpartially said housing.

According to another embodiment, these holding means are formed of anadded-on clip closing partially the reception housing of nut.

In the latter embodiment, the clip for holding a nut is advantageouslyin the form of an open circular loop; this loop comprises a snap-ongroove which co-operates with a throat of appropriate shape provided inthe integration housing of the nut.

According to another characteristic, the means for locking the nut inrotation in the reception housing of the supporting structure are formedof at least one relief laid out on one of said parts (nut or supportingstructure), co-operating with an adapted notch, provided on the otherpart (supporting structure or nut).

According to a particular embodiment, the implant includes cylindricalcontact surfaces between the screw head and the supporting structure, onthe one hand, and between the supporting structure and the nut, on theother hand. These cylindrical contact surfaces are adapted to confer tothe fastening screw a possibility of orientation relative to thesupporting structure, while keeping contacts between surfaces(cylindrical contacts) enabling to optimise the connection duringclamping.

Preferably these cylindrical contact surfaces have the same axis.

According to a preferred embodiment, the implant includes sphericalcontact surfaces between the screw head and the supporting structure, onthe one hand, and between the supporting structure and the nut, on theother hand, which are adapted to confer to the fastening screw apossibility of orientation relative to the supporting structure, whilekeeping contacts of surfaces (spherical contacts). This particularityconfers important possibilities for angular adjustment of the screw andoptimises the mechanic connection during clamping.

Preferably these spherical contact surfaces, in form of spherical capshave the same centre.

To obtain a compact assembly and having an interesting capacity ofangular adjustment of the screws, the axis or the centre of thecylindrical or spherical contact surfaces, is situated in the vicinityof the upper plane of the supporting structure, or is confused with thisplane.

According to still another particularity, the orthopaedic implantcomplying with the invention includes a nut containing a cylindricalshaft exhibiting a female thread and a spherical cap or crown situatedat the periphery of said cylindrical shaft.

According to still another particularity, the fastening screw is fittedwith a body thread able to co-operate with the receiving bone material,and of a head thread able to co-operate with the associated nut, theouter diameter of the body thread being smaller than or equal to theouter diameter of the head thread to let the screw through the nut.

For optimised clamping, the fastening screw(s) are advantageously fittedwith a head thread composed of n threads offset by 1/n turns, andwhereof the pitch co-operates with that of the thread of the nut and tothat of the body thread.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further illustrated, without being limitedthereto, by the following description of several particular embodiments,given solely for exemplification purposes and represented on theappended drawings whereon:

FIG. 1 represents generally an orthopaedic plate positioned at thesurface of a fractured bone, and intended to receive fastening screws;

FIG. 2 is a functional flow chart of a first possible embodiment of animplant of the present invention;

FIG. 3 illustrates a top view of a possible embodiment of an orificelaid out in the supporting structure to let through a fastening screw;

FIGS. 4 to 7 illustrate four different functional flow charts ofimplants of the present invention, authorising angular adjustments ofthe axis of the screw relative to the supporting structure;

FIG. 8 is an exploded sectional view, of a preferred embodiment ofimplant of the functional flow chart of FIG. 7;

FIG. 9 shows the implant of FIG. 8, upon complete straight screwing,i.e. the screw is centred on the axis of the orifice of the support;

FIG. 10 shows the same implant as FIG. 9 but upon complete tiltingclamping, i.e. the screw forms an angle with the axis of the orifice ofthe support;

FIG. 11 is a large-scale partial view, of the underside of thesupporting structure showing the reception housing of the nut;

FIG. 12 is a sectional view according to 12-12 of FIG. 11;

FIG. 13 is also a large-scale perspective view, of a nut for the implantillustrated on FIGS. 8 to 10;

FIG. 14 is a view of the upperside of the nut illustrated on FIG. 13;

FIG. 15 is a diametrically sectional view according to 15-15 of FIG. 14;

FIG. 16 is a lateral view of the nut illustrated on FIGS. 13 to 15;

FIG. 17 is a large-scale perspective view of the circular clip enablingto hold the nut in the housing of the supporting structure;

FIG. 18 is a top view of the clip illustrated on FIG. 17;

FIG. 19 is a diametrically sectional view of the clip according to 19-19of FIG. 18.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the orthopaedic implant 0 formed of a supporting structurein the form of an osteosynthesis plate 1 positioned on a fractured bone2, for example, an epiphysis of the radius, and exhibiting four circularorifices 3 for accommodating the fastening screws 5. Each screw 5includes a screw head 6 and a screw body 8.

FIG. 1 also illustrates the drilling gun 9 which is used before placingthe screws 5 in order to drill positioning holes in the bone material,through the orifices 3.

FIG. 2 is a functional flow chart which shows schematically the assemblyof a screw 5 on the supporting plate 1.

On this figure, one may note the presence of un nut 10 positioned in ahousing 12 laid out in the supporting plate 1, so that upon completescrewing of said plate 1 is sandwiched between the head 6 of the screw 5and said nut 10. The female thread of the nut 10 co-operates with themale thread of the screw body 8 to lock the assembly upon completescrewing.

To this end, the screw 5 may include a single thread, on the one handfor anchoring in the bone material, and on the other hand forco-operation with the nut; but it may also be fitted with two differentthreads each ensuring one of the functions aforementioned.

The nut 10 may be simply integrated partially in the housing 12. It isheld in place in said housing 12, facing the orifice 3, by appropriateholding means 13, and it is also locked in rotation by appropriate meansrepresented in the form of a simple line marked 14.

The holding means 13 may be in the form of a material rebound or of anadded-on structure detailed below, of the locking clip type,implemented, after positioning the nut 10 in the housing 12.

The rotation of the nut 10 is locked either by the general relativeshapes of the nut 10 and of the reception housing 12, or by co-operationof complementary members such as relief(s) and notch(es), laid out onthe surfaces facing the nut and of the housing.

According to the invention, the contours of the housing 12 and thecontours of the nut 10 are adapted and sized to confer to the latter, insaid housing, at least one degree of freedom, greater than that of asimple functional clearance, thereby enabling self-centring of the screw5 and of the nut 10, and this regardless of the admissible orientationof the axis of said screw relative to the axis of the housing 3.

FIG. 2 shows both lines of axes 15 illustrating the amplitude ofpossible corresponding inclinations of the screws. The middle position,normal to the supporting plate 1 is represented by the axis 16, whichaxis 16 corresponds to the axis of the housing 3.

As represented on FIG. 3, the supporting plate 1 may include elongatedorifices 3′ thereby giving a possibility of additional longitudinaladjustment of the screws 5 with respect to the support 1. Theseelongated orifices 3′ may have a general rectilinear or curvilinearshape.

FIGS. 4, 5, 6 and 7 are functional diagrams derived from that of FIG. 2,illustrating the screwed assembly of the invention, but with cylindricalor spherical contact surfaces between the screw head 6 and thesupporting plate 1, on the one hand, and between the supporting plate 1and the nut 10, on the other hand, authorising a degree of freedom andrelatively important angular adjustment possibilities of the screw 5,while keeping a significant contact surface promoting good cohesion ofthe assembly after screwing.

In all cases, the different parts are shaped as well as possible toobtain significant angular adjustment possibilities and to keep the bestpossible contacts between surfaces. In the case of cylindrical contactsurfaces, the angular adjustment is possible in a plane if the orifice 3is circular, or in different parallel planes corresponding to aprismatic volume if an oblong orifice 3′ as illustrated on FIG. 3 isavailable.In the case of spherical contact surfaces, there is preferably acircular reception orifice and the angular adjustment of the screw isthen possible within a conical volume whereof the axis is confused withthat of the circular orifice 3.

On FIG. 4, the head 6 of the screw 5 is en contact with an intermediatemember 18 which comprises a slipping surface in contact with thesupporting plate 1. The contact surfaces between the head 6 and thisadded-on member 18 correspond to a cylindrical portion centred on anaxis 19, or to a spherical cap centred at a point 19, as the case maybe. The axis or the centre 19 is here positioned on the outside, abovethe supporting plate 1.

On the other hand, the nut 10 and the supporting plate 1 are also incontact on cylindrical or spherical surfaces, as the case may be. Theaxis or the centre 20 of the cylindrical portion or of the correspondingportion of spherical cap is here positioned on the inside, i.e. on thebone structure side.

The nut 10 is held in place by the means 13 and it is locked in rotationby means 14 schematised in the form of a simple line.

FIGS. 5, 6 and 7 illustrate embodiments deprived of complementary part18 and whereof the spherical or cylindrical contact surfaces of thescrew/supporting plate and supporting plate/nut are centred on the sameaxis or exhibit the same centre.

For the embodiment illustrated on FIG. 5, the axis or the correspondingcentre 21 is situated between both contact surfaces.

For the embodiment illustrated on FIG. 6, the axis or the correspondingcentre 22 is situated on the inner face of the supporting structure 1.

For the embodiment of FIG. 7, the axis or the corresponding centre 23 issituated on the outer face of the supporting structure 1.

The embodiment illustrated on FIG. 7 appears more compact. Preferably,the axis or the centre 23 is situated in the vicinity of the uppersurface of the supporting structure 1 to enhance the possibilities ofangular bottoming of the screw 5; the distance marked H on this figuretends then towards zero value.

In all cases, the nut 10 is held in its housing 12 by means 13 such asmaterial rebound or clip as detailed below, and it is locked in rotationby means represented schematically in the form of a simple line 14 alsodetailed below.

Because of the general space requirements of the parts, thecorresponding angular clearance cone always confers to the practicianinteresting adjustment possibilities.

FIGS. 8 to 19 detail an embodiment according to that representeddiagrammatically on FIG. 7.

FIG. 8 represents a fastening screw 5 as a longitudinal diagrammaticalsection. This screw 5 shows on the one hand a screw body 8 fitted with athread 25 and whereof the end 26 is pigtail-shaped, and on the otherhand a screw head 6 fitted with one clean thread 27. The upper sectionof the screw head 6 contains a cavity 29 with polygonal wallsco-operating with the setting auxiliary device.

This screw head 6 shows at its end a collar whereof the peripheralcontour is in the form of a spherical crown 7, intended to make contactwith a surface of equivalent shape provided on the supporting structure1.

The screw 5 runs through the plate 1, seen as a sectional view, at thecircular orifice 3, as well as the nut 10 and the holding means 13, herein the form of a locking clip, also seen as a sectional view.

The supporting structure 1, the nut 10 and the locking clip 13 arerepresented in exploded views, separate from one another.

The thread 27 of the screw head 5 is adapted to that of the nut 10. Thisthread is composed of n threads 28 offset by 1/n turn, whereof the pitchis able to co-operate with that of the thread 30 of the nut 10, whichpitch corresponds to that of the thread 25 of the screw body 8.

The thread 25 of the screw body 8 may be anchored by screwing in thebone material; the outer diameter of this body thread 25 is smaller thanor equal to the outer diameter of the head thread 27 to let the screwbody 8 through the threaded orifice of the nut 10.

FIG. 9 represents the fastening screw 5 upon complete screwing, in aconfiguration normal to the plate 1 (the bone reception structure is notrepresented). The plate 1 is then sandwiched between on the one hand thescrew head 6, and on the other hand the nut 10 whereof the female thread30 co-operates with the male thread 27 of said screw head 6.

FIG. 10 represents the fastening screw 5 upon complete screwing in aconfiguration tilted relative to the axis 16 of the orifice 3.

This tilting possibility is due to the fact that the nut 10 has a degreeof freedom in its reception housing 12. On the other hand, the sphericalcontact surfaces of the screw head/supporting plate and supportingplate/nut enable to obtain high clamping quality regardless of theadmissible tilt of the axis of the screw 5 relative to the axis 16 ofthe orifice 3.

One may also provide a spherical contact surface between the nut 10 andthe locking clip 13 for better guiding of the nut 10 when positioningthe screw 5 when starting the screwing process.

The corresponding contact surfaces are detailed below in connection withthe description of each constitutive part of the implant.

FIGS. 11 and 12 represent in detail the configuration of the circularorifice 3 and of the housing 12 which is laid out in the supportingstructure 1, which housing 12 is intended to receive the nut 10 detailedon FIGS. 13 to 16. This nut 10 is held preferably by a locking clipdetailed on FIGS. 17 to 19, which clip enables easier disassembly of thenut than when said nut is crimped in position.

As represented on FIGS. 11 and 12, the supporting plate 1 includes aspherical ring 312 formed of a first spherical crown 31 for contact withthe screw head 6, and of a second spherical crown 32 for contact withthe nut 10.

The peripheral portion 313 which extends between both spherical crowns31 and 32, is of truncated form, with sufficient angle to allow movementof the nut 10 and hence of the screw 5 relative to the supporting part1. This portion 313 may form a stop for the nut 10 and in particular forits shaft 100 as detailed below.

On the circular periphery of the housing 12, one may note the presenceof a circular throat 33 intended for positioning and locking theretaining clip 13.

The means locking the rotation of the nut 10 with respect to the support1 are formed of at least one toe or tang. FIG. 11 shows three tangs 34distributed regularly in the bottom of the circular housing 12, betweenthe periphery of said housing and the spherical crown 32. These tangs 34co-operate with homologue female shapes detailed below, provided on thenut 10 for locking the latter in rotation.

As represented on FIGS. 13 to 16, the nut 10 has a spherical crown 35intended for contact with the supporting structure 1 and in particularthe spherical crown 32 of the ring 312. One may also provide an externalspherical crown 36 intended for contact with the holding clip 13. Saidspherical crowns 35, 36 are part of a spherical ring 356 connected tothe lower periphery of a cylindrical shaft 100 serving as a nut, whichshaft is fitted with the female thread 30.

The external peripheral surface of the shaft 100 is accommodated with acertain clearance in the truncated portion 313 of the support 1, so asnot to alter the ball-joint spherical contacts between the nut 10 andsaid support.

The amplitude of the movement of the nut 10 with respect to the support1 may be limited by the truncated portion 313 of said support, whichacts as a stop for the shaft 100 of the nut 10.

The spherical surface 36 optimises the correct spatial positioning ofthe nut when introducing the screw 5. The degree of freedom of the nut10 in its reception housing 12 enables self-centring of the fasteningscrew 5 and of the associated nut when fastening the implant.

On FIGS. 13 and 14, one may see the female shapes, aforementioned, inthe form of cavities or notches 37 which are designed for co-operatingwith the tangs 34 of the supporting structure 1 in order to lock the nut10 in rotation. The sides of these cavities or notches 37 may beparallel or slightly divergent, as illustrated on FIGS. 13, 14 and 15.

In the exemplary embodiment illustrated, the tangs 34 and the homologuenotches 37 are three in number, laid out at 120° respectively in thebottom of the housing 12 of the supporting structure 1, and at theperiphery of the nut 10. Cutting the spherical crown 356 using thenotches 37 confers certain elasticity to the nut 10.

As represented on FIGS. 17 to 19, the clip 13 is in the form of acircular ring fitted with a slot 38 providing thereby certain radialelasticity. On its external periphery, this clip 13 is fitted with aperipheral rib or emboss 39 which may be imbedded in the circular throat33 of the housing 12 laid out in the support 1. Imbedding the clip 13 onthe supporting structure 1 is made possible by the presence of the slot38. The clip 13 is sized for holding the nut 10 in the housing 12.

The clip 13 is also fitted internally with a spherical crown 40 able toco-operate with the corresponding spherical crown 36 provided on the nut10.

As mentioned before, upon complete screwing of the fastening screw 5,the different spherical crowns: —7 on the head 6 of the screw 5, —31 and32 on the support 1, and —35 and 36 on the nut 10, are concentric; onethe assembly complete, the corresponding centre 23 is positionedsubstantially in the plane of the upper surface of the supporting plate1, as shown on FIG. 9.

1. An implantable orthopedic device comprising: a) a supportingstructure comprising: 1) an upper face; 2) a lower face; and 3) at leastone housing defined in the supporting structure, each said housing beingpartially defined by an upper spherical ring and partially closed by alower holding element, each said upper spherical ring, housing, andlower holding element defining an orifice centered about an axis; b) atleast one nut, made in one piece, comprising a female thread and aspherical contact surface, each said nut being shaped so as to be heldwithin a respective one of the housings, between said upper sphericalring and said lower holding element; c) at least one fastening screw,each comprising: 1) a threaded body sized so that the threaded body canpass through the orifice, the threaded body comprising a body threadproportioned to be able to cooperate with bone material; and 2) a headsized to prevent the head from passing through the orifice, the headcomprising: A) a collar having a peripheral contour in the form of aspherical contact surface; and B) head thread that is sized to engagethe female thread of the nut, an outer diameter of the head thread beinggreater than or equal to an outer diameter of the body thread, the headthread being disposed between the collar and the body thread; and d) atleast one relief and an adapted notch, one of which is disposed on thehousing, another of which is disposed on the nut, the nut being, in theabsence of engagement of the fastening screw, free to move within apredetermined tilting range to allow an axis of the female thread to betilted with the respect to the axis of the upper spherical ring; whereineach said upper spherical ring comprises upper and lower sphericalcontact surfaces, having a same center, the upper and lower sphericalcontact surfaces being arranged to cooperate with said spherical contactsurfaces of said screw head and said nut, respectively; and wherein eachsaid spherical ring, nut, and fastening screw are designed so that eachsaid fastening screw can be passed through a respective one of theorifices and threaded through a corresponding said nut so as to clampthe spherical ring between the nut and the screw head at a selectedangle within the tilting range and while keeping contact between saidcorresponding spherical contact surfaces; and wherein the notch andrelief are positioned and sized so that, even when the fastening screwis not engaged with the nut, the nut is locked in the housing to preventrotation about an axis of the female thread.
 2. The implantable deviceof claim 1, wherein the holding element comprises a clip that partiallycloses the housing.
 3. The implantable device of claim 2, wherein theclip is an open circular loop that comprises a snapon groove cooperatingwith a throat in the housing.
 4. The implantable device of claim 1,wherein the cylindrical contact surfaces between the screw head and thesupporting structure, and the cylindrical contact surfaces between thesupporting structure and the nut have a same orientation axis.
 5. Theimplantable device of claim 4, wherein the cylindrical contact surfacesare arranged so that the orientation axis is situated in a vicinity ofan upper plane of the supporting structure.
 6. The implantableorthopedic device of claim 1, wherein the upper spherical ring extendsinward from the upper face of the supporting structure.